It's true that someone has to be coaching multiple positions. There are a lot of ways to mix & match.
We do need a "QB guy" on the staff, however. I think every team does if they are to expect quality QB play. When we had Watson, this wasn't an issue, as Watson was clearly a OC/QB guy with specialty in working with QBs.
With Beck, it's not clear that this is his specialty and I don't think it is. We do still have that QB guy, though, and it's currently Joe Ganz, who has to be considered a lot more inexperienced than Watson at least, and also won't be here next year.
We're going to need someone to take over the "QB guy" role next year, and I hope it's a full-time assistant who is also a recruiting asset and works with another area of the offense as well, whether that's run game coordinating, WRs, TEs, RBs, whatever -- and shuffle the staff as needed to accomodate.